Various mixtures of substances are separated by conducting distillation processes within distillation columns. The separation is conducted by contacting an ascending vapor phase of the mixture with a descending liquid phase. As a result of such contact, the ascending vapor phase becomes ever more rich in the more volatile or light components as it ascends and the descending liquid phase becomes ever more rich in the less volatile or heavy components as it descends.
Packings can be used to facilitate the contact of the liquid and vapor mixture phases within the distillation column that can be of either of the random or structured type of packing. In random packings, individual packing elements are located in packing beds. In structured packing, corrugated sheets of packing are provided in an arrangement where the corrugations cross one another. In both types of packings, the descending liquid phase forms a descending film on the outer surfaces thereof that is contacted by the ascending vapor phase. In structured packing, the crossing of the corrugations helps to distribute the contact in a transverse direction to the column access. Typically, the structured packing is deployed in an arrangement where an overlying layer of corrugated sheets is oriented at right angles to an underlying layer of corrugated sheets.
The number of beds of packing will of course depend on the type of distillation being conducted and the substances to be separated. However, as between packing beds, the descending liquid is collected from an overlying packing bed by a liquid collector and the collected liquid is then distributed to an underlying backing bed by a liquid distributor connected to the liquid collector. The liquid collector and liquid distributor are designed to allow the ascending vapor phase to pass from the underlying packing bed to the overlying packing bed. When the descending liquid leaves a packing bed, the liquid may have a varying concentration of substances as viewed in a transverse direction. It is desired, however, that the concentration of substance be as uniform as possible so that the distillation column can function at a level consistent with its design. Therefore, it is desired to thoroughly mix the liquid before introducing it to the underlying packing bed. Additionally, it is also desired that the liquid collector and liquid distributor are designed so that they produce a low pressure drop for the ascending vapor as the vapor passes through such column internals so that upward vapor flow is not impeded.
A typical form of a collector is a chimney tray collector in which a deck-like plate is provided with rows of chimneys situated on either side of an open rectangular sump to allow the ascending vapor to flow through the deck-like plate. The chimneys are capped with hats that that collect part of the descending liquid and direct the same into the open rectangular sump. Another part of the liquid is collected on the deck-like plate between the chimneys and is directed into the open rectangular sump. The open rectangular sump has a bottom opening that is connected by a conduit to the liquid distributor. A known form of a liquid distributor is a channel-type distributor having open, distribution channels connected to a central header. An open pre-distribution box is situated within the header to receive liquid from the liquid collector and distribute the liquid to the central header. The distribution channels and the central header are provided with perforate bottom walls to distribute the liquid across the distillation column to an underlying packing bed. Open spaces between the distribution channels permit the vapor to flow to the chimneys in the liquid collector.
As can be appreciated, a liquid distributor and collector, such as described above take up space within a distillation column and represent part of the required height of the column. As could be appreciated by those skilled in the art, taller distillation columns are more expensive to fabricate than more compact columns. Further, taller the columns require more expensive supporting structures and equipment such as cold boxes for cryogenic distillations and longer piping runs and etc. In order to decrease the height requirements imposed by separate collectors and distributors, combined liquid collectors and distributors have been produced. An example of such a device is disclosed in U.S. Pat. No. 5,645,770 in which hats are placed on a series of chimneys mounted on a tray. The hats are oriented to direct the descending liquid to opposite sides of the plate. Liquid is discharged from distribution channels located at the bottom of the tray or from openings in the bottom of the tray. In the combined collector and distributor of this patent, the flow of ascending vapor is somewhat impeded given that the ascending vapor is constrained to pass through an array of chimneys. Furthermore, given that the collected liquid is distributed to opposite sides of the distillation column shell by the hats, the degree to which liquid mixing occurs is limited to a center through located in the bottom of the distributor portion of the device.
As will be discussed, the present invention provides a combined liquid collector and distributor having a lower resistance to the up flow of the ascending vapor than the prior art and that provides a greater degree of mixing than is possible with similar prior art devices.